Is there life elsewhere in the Milky Way
the possibility of Earth-like planets forming elsewhere, we must go back to the beginning of the Universe, to the big bang to discover how Earth formed. After the big bang, space started expanding and cooling. Just one second after the big bang, the universe was filled with a mixture of protons, electrons, neutrons, positrons and neutrinos. After 100,000 years, matter cooled to the point that free electrons managed to become entrapped in orbits around positive nuclei, forming hydrogen and helium gas. 4 This gas then formed into clusters which formed galaxies, these subdivided to form the billions of stars observable today. Through the course of the Milky Way’s history, o ver 100 million red giant stars have formed and exploded converting 2% of our galaxy’s hydrogen and helium to form the heavier elements of carbon, oxygen, iron, magnesium, silicon, and more that were required to form Earth, through a process called nucleosynthesis. Nucleosynthesis occurs at high temperatures and pressures in the centres of stars, and new elements emerge from the merging of helium atoms. Three helium atoms merge creating carbon; carbon and heliummerges, forming oxygen; two carbon atoms will merge to form magnesium, and so on. 5 Nucleosynthesis occurred across the galaxy, so there is an abundance of Earth-sized rocky planets. In addition to having a solid and liquid exterior, a habitable planet must be in a habitable zone known as the ‘Goldilocks Zone’ from its star, just close enough that water cannot freeze, yet far enough that water cannot evaporate.
Further conditions for life include:
The planet having plate tectonics
•
Amagnetic field
•
Fellow giant gas planets
•
• Being large enough to maintain an atmosphere of specific composition • Having a favourable surface temperature
A planet, if it is large enough, can form an atmosphere that has a strong enough gravitational force upon the gases to prevent them from escaping. The velocity of a particle needed to escape Earth's atmosphere is 11.2 km/sec, whilst Jupiter’s escape velocity is 60 km/sec, and the moon’s escape velocity is just 2.4 km/sec, hence why the moon has no atmosphere because all the gases require less energy to escape. This explains the formation of Earth’s and Venus’s atmosphere, as they are similarly sized. Earth’s magnetic field has countered the stripping of the atmosphere by diverting charged particles from the sun, which are hazardous to life, around the planet. Earth initially developed an atmosphere very different in composition to the one we have today. Our planet’s early atmosphere con sisted of mainly carbon dioxide, hydrogen sulphide and methane, with almost no oxygen, due to the nature of o xygen’s high reactivity. This favours initial life, as life requires carbon to form, and used the carbon dioxide in the atmosphere to create the first cells whilst oxygen was in fact poisonous to initial primitive life. There is also evidence of liquid water on Earth from as
4 Sawyer (n.d.). 5 Tate 2010.
186
Made with FlippingBook - Online catalogs